1. Field of the Invention
The present invention relates generally to the field of antifriction bearings for use in mechanical systems. More particularly, the invention relates to a technique for rendering bearing components corrosion-resistant for use in food and beverage, chemical, marine, and similar potentially corrosive applications.
2. Description of the Related Art
A wide variety of applications exist in all technical fields for antifriction bearings used in rotary equipment. In general, in rotary applications, such bearings are used to reduce frictional contact between a rotary member and a stationary member, or between two rotating elements. In many applications, one of the elements may be fixed to a support structure, such as a machine housing or frame. The bearing is mounted to the support structure via a bearing housing and receives the rotating element in a central aperture. Rotating elements are typically configured as shafts, shaft extensions, hubs, and the like. In many applications one of several relatively standard housings may be employed, providing the desired support for the bearing and shaft, with the bearing being received in one of a number of ways within a recess provided in the housing.
A number of applications exist for antifriction bearings in environments which may degrade, corrode or otherwise attack the bearing components, as well as other elements of the mechanical transmission system. For example, in many chemical and marine environments, water, and other liquids, as well as trace chemicals such as salts, corrosives, acids, and the like in the air surrounding the bearings may chemically attack the bearing components. In other applications, such as in the food and beverage industry, frequent wash downs of production or processing lines with water and detergents or high pressure steam may both chemically and mechanically attack the bearings components. In either case, degradation of the bearing components may take the form of oxidation products, such as white or red rust on ferrous substrates. In applications such as those in the food and beverage industry, this degradation is unacceptable, and may call for immediate replacement of affected bearings, leading to additional expense and possible down time.
Several conventional approaches have been developed to inhibit, or at least to forestall bearing component degradation in demanding application environments. In one relatively simple solution, expensive and somewhat exotic materials may be employed in the components which make them less susceptible to common corrosion. For example, in antifriction bearings, components such as collars, races, balls, rollers, and so forth, may be made of stainless steel or a similar corrosion-resistant metal. Moreover, bearing components may be plated with galvanic layers, such as layers including cadmium or zinc, sometimes alloyed with other metals. Such plated layers act as sacrificial materials which corrode before the underlying substrate, thereby forestalling eventual replacement of the bearing. In another common technique, mechanical plated layers, such as chrome, may be applied to the substrate to provide an aesthetically pleasing outer appearance, as well as a mechanical barrier to corrosive products.
While such solutions to rendering antifriction bearings corrosion-resistant are often effective, they are not without drawbacks. For example, materials such as stainless steel can be cost prohibitive for a number of applications and, consequently, their use is often limited to cases of actual need where such high costs are justified. Galvanic plating is also useful, but may lead to undesirable environmental considerations, particularly disposal of solutions and other processing by-products, such as in the case of cadmium, or to problems with appearance and wear, as in the case of certain zinc and zinc alloy plating techniques. Finally, mechanical layers such as chrome require fairly specialized and somewhat costly plating processes, and can also result in relatively undesirable by-products.
There is a need, therefore, for improved corrosion-resistant bearings and bearing components which avoids these drawbacks of heretofore known structures. There is a particular need at present for a cost-effective process for rendering bearing components corrosion-resistant, which can be applied in a relatively straightforward manner, which wears well, and which provides an aesthetically pleasing product, both upon installation and during a reasonable useful life.